12 How to Get Your Change Into the Linux Kernel
3 or
4 Care And Operation Of Your Linus Torvalds
5678For a person or company who wishes to submit a change to the Linux
9kernel, the process can sometimes be daunting if you're not familiar
10with "the system." This text is a collection of suggestions which
11can greatly increase the chances of your change being accepted.
1213Read Documentation/SubmitChecklist for a list of items to check
14before submitting code. If you are submitting a driver, also read
15Documentation/SubmittingDrivers.
1617Many of these steps describe the default behavior of the git version
18control system; if you use git to prepare your patches, you'll find much
19of the mechanical work done for you, though you'll still need to prepare
20and document a sensible set of patches.
2122--------------------------------------------
23SECTION 1 - CREATING AND SENDING YOUR CHANGE
24--------------------------------------------
252627281) "diff -up"
29------------
3031Use "diff -up" or "diff -uprN" to create patches. git generates patches
32in this form by default; if you're using git, you can skip this section
33entirely.
3435All changes to the Linux kernel occur in the form of patches, as
36generated by diff(1). When creating your patch, make sure to create it
37in "unified diff" format, as supplied by the '-u' argument to diff(1).
38Also, please use the '-p' argument which shows which C function each
39change is in - that makes the resultant diff a lot easier to read.
40Patches should be based in the root kernel source directory,
41not in any lower subdirectory.
4243To create a patch for a single file, it is often sufficient to do:
4445 SRCTREE= linux-2.6
46 MYFILE= drivers/net/mydriver.c
4748 cd $SRCTREE
49 cp $MYFILE $MYFILE.orig
50 vi $MYFILE # make your change
51 cd ..
52 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
5354To create a patch for multiple files, you should unpack a "vanilla",
55or unmodified kernel source tree, and generate a diff against your
56own source tree. For example:
5758 MYSRC= /devel/linux-2.6
5960 tar xvfz linux-2.6.12.tar.gz
61 mv linux-2.6.12 linux-2.6.12-vanilla
62 diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
63 linux-2.6.12-vanilla $MYSRC > /tmp/patch
6465"dontdiff" is a list of files which are generated by the kernel during
66the build process, and should be ignored in any diff(1)-generated
67patch. The "dontdiff" file is included in the kernel tree in
682.6.12 and later.
6970Make sure your patch does not include any extra files which do not
71belong in a patch submission. Make sure to review your patch -after-
72generated it with diff(1), to ensure accuracy.
7374If your changes produce a lot of deltas, you need to split them into
75individual patches which modify things in logical stages; see section
76#3. This will facilitate easier reviewing by other kernel developers,
77very important if you want your patch accepted.
7879If you're using git, "git rebase -i" can help you with this process. If
80you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
81is another popular alternative.
828384852) Describe your changes.
8687Describe your problem. Whether your patch is a one-line bug fix or
885000 lines of a new feature, there must be an underlying problem that
89motivated you to do this work. Convince the reviewer that there is a
90problem worth fixing and that it makes sense for them to read past the
91first paragraph.
9293Describe user-visible impact. Straight up crashes and lockups are
94pretty convincing, but not all bugs are that blatant. Even if the
95problem was spotted during code review, describe the impact you think
96it can have on users. Keep in mind that the majority of Linux
97installations run kernels from secondary stable trees or
98vendor/product-specific trees that cherry-pick only specific patches
99from upstream, so include anything that could help route your change
100downstream: provoking circumstances, excerpts from dmesg, crash
101descriptions, performance regressions, latency spikes, lockups, etc.
102103Quantify optimizations and trade-offs. If you claim improvements in
104performance, memory consumption, stack footprint, or binary size,
105include numbers that back them up. But also describe non-obvious
106costs. Optimizations usually aren't free but trade-offs between CPU,
107memory, and readability; or, when it comes to heuristics, between
108different workloads. Describe the expected downsides of your
109optimization so that the reviewer can weigh costs against benefits.
110111Once the problem is established, describe what you are actually doing
112about it in technical detail. It's important to describe the change
113in plain English for the reviewer to verify that the code is behaving
114as you intend it to.
115116The maintainer will thank you if you write your patch description in a
117form which can be easily pulled into Linux's source code management
118system, git, as a "commit log". See #15, below.
119120Solve only one problem per patch. If your description starts to get
121long, that's a sign that you probably need to split up your patch.
122See #3, next.
123124When you submit or resubmit a patch or patch series, include the
125complete patch description and justification for it. Don't just
126say that this is version N of the patch (series). Don't expect the
127patch merger to refer back to earlier patch versions or referenced
128URLs to find the patch description and put that into the patch.
129I.e., the patch (series) and its description should be self-contained.
130This benefits both the patch merger(s) and reviewers. Some reviewers
131probably didn't even receive earlier versions of the patch.
132133Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
134instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
135to do frotz", as if you are giving orders to the codebase to change
136its behaviour.
137138If the patch fixes a logged bug entry, refer to that bug entry by
139number and URL. If the patch follows from a mailing list discussion,
140give a URL to the mailing list archive; use the https://lkml.kernel.org/141redirector with a Message-Id, to ensure that the links cannot become
142stale.
143144However, try to make your explanation understandable without external
145resources. In addition to giving a URL to a mailing list archive or
146bug, summarize the relevant points of the discussion that led to the
147patch as submitted.
148149If you want to refer to a specific commit, don't just refer to the
150SHA-1 ID of the commit. Please also include the oneline summary of
151the commit, to make it easier for reviewers to know what it is about.
152Example:
153154 Commit e21d2170f36602ae2708 ("video: remove unnecessary
155 platform_set_drvdata()") removed the unnecessary
156 platform_set_drvdata(), but left the variable "dev" unused,
157 delete it.
158159If your patch fixes a bug in a specific commit, e.g. you found an issue using
160git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
161SHA-1 ID, and the one line summary.
162Example:
163164 Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
165166The following git-config settings can be used to add a pretty format for
167outputting the above style in the git log or git show commands
168169 [core]
170 abbrev = 12
171 [pretty]
172 fixes = Fixes: %h (\"%s\")
1731743) Separate your changes.
175176Separate _logical changes_ into a single patch file.
177178For example, if your changes include both bug fixes and performance
179enhancements for a single driver, separate those changes into two
180or more patches. If your changes include an API update, and a new
181driver which uses that new API, separate those into two patches.
182183On the other hand, if you make a single change to numerous files,
184group those changes into a single patch. Thus a single logical change
185is contained within a single patch.
186187If one patch depends on another patch in order for a change to be
188complete, that is OK. Simply note "this patch depends on patch X"
189in your patch description.
190191If you cannot condense your patch set into a smaller set of patches,
192then only post say 15 or so at a time and wait for review and integration.
1931941951964) Style check your changes.
197198Check your patch for basic style violations, details of which can be
199found in Documentation/CodingStyle. Failure to do so simply wastes
200the reviewers time and will get your patch rejected, probably
201without even being read.
202203At a minimum you should check your patches with the patch style
204checker prior to submission (scripts/checkpatch.pl). You should
205be able to justify all violations that remain in your patch.
2062072082095) Select e-mail destination.
210211Look through the MAINTAINERS file and the source code, and determine
212if your change applies to a specific subsystem of the kernel, with
213an assigned maintainer. If so, e-mail that person. The script
214scripts/get_maintainer.pl can be very useful at this step.
215216If no maintainer is listed, or the maintainer does not respond, send
217your patch to the primary Linux kernel developer's mailing list,
218linux-kernel@vger.kernel.org. Most kernel developers monitor this
219e-mail list, and can comment on your changes.
220221222Do not send more than 15 patches at once to the vger mailing lists!!!
223224225Linus Torvalds is the final arbiter of all changes accepted into the
226Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
227He gets a lot of e-mail, so typically you should do your best to -avoid-
228sending him e-mail.
229230Patches which are bug fixes, are "obvious" changes, or similarly
231require little discussion should be sent or CC'd to Linus. Patches
232which require discussion or do not have a clear advantage should
233usually be sent first to linux-kernel. Only after the patch is
234discussed should the patch then be submitted to Linus.
2352362372386) Select your CC (e-mail carbon copy) list.
239240Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
241242Other kernel developers besides Linus need to be aware of your change,
243so that they may comment on it and offer code review and suggestions.
244linux-kernel is the primary Linux kernel developer mailing list.
245Other mailing lists are available for specific subsystems, such as
246USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
247MAINTAINERS file for a mailing list that relates specifically to
248your change.
249250Majordomo lists of VGER.KERNEL.ORG at:
251 <http://vger.kernel.org/vger-lists.html>
252253If changes affect userland-kernel interfaces, please send
254the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
255a man-pages patch, or at least a notification of the change,
256so that some information makes its way into the manual pages.
257258Even if the maintainer did not respond in step #5, make sure to ALWAYS
259copy the maintainer when you change their code.
260261For small patches you may want to CC the Trivial Patch Monkey
262trivial@kernel.org which collects "trivial" patches. Have a look
263into the MAINTAINERS file for its current manager.
264Trivial patches must qualify for one of the following rules:
265 Spelling fixes in documentation
266 Spelling fixes which could break grep(1)
267 Warning fixes (cluttering with useless warnings is bad)
268 Compilation fixes (only if they are actually correct)
269 Runtime fixes (only if they actually fix things)
270 Removing use of deprecated functions/macros (eg. check_region)
271 Contact detail and documentation fixes
272 Non-portable code replaced by portable code (even in arch-specific,
273 since people copy, as long as it's trivial)
274 Any fix by the author/maintainer of the file (ie. patch monkey
275 in re-transmission mode)
2762772782797) No MIME, no links, no compression, no attachments. Just plain text.
280281Linus and other kernel developers need to be able to read and comment
282on the changes you are submitting. It is important for a kernel
283developer to be able to "quote" your changes, using standard e-mail
284tools, so that they may comment on specific portions of your code.
285286For this reason, all patches should be submitting e-mail "inline".
287WARNING: Be wary of your editor's word-wrap corrupting your patch,
288if you choose to cut-n-paste your patch.
289290Do not attach the patch as a MIME attachment, compressed or not.
291Many popular e-mail applications will not always transmit a MIME
292attachment as plain text, making it impossible to comment on your
293code. A MIME attachment also takes Linus a bit more time to process,
294decreasing the likelihood of your MIME-attached change being accepted.
295296Exception: If your mailer is mangling patches then someone may ask
297you to re-send them using MIME.
298299See Documentation/email-clients.txt for hints about configuring
300your e-mail client so that it sends your patches untouched.
3013028) E-mail size.
303304When sending patches to Linus, always follow step #7.
305306Large changes are not appropriate for mailing lists, and some
307maintainers. If your patch, uncompressed, exceeds 300 kB in size,
308it is preferred that you store your patch on an Internet-accessible
309server, and provide instead a URL (link) pointing to your patch.
3103113123139) Name your kernel version.
314315It is important to note, either in the subject line or in the patch
316description, the kernel version to which this patch applies.
317318If the patch does not apply cleanly to the latest kernel version,
319Linus will not apply it.
32032132232310) Don't get discouraged. Re-submit.
324325After you have submitted your change, be patient and wait. If Linus
326likes your change and applies it, it will appear in the next version
327of the kernel that he releases.
328329However, if your change doesn't appear in the next version of the
330kernel, there could be any number of reasons. It's YOUR job to
331narrow down those reasons, correct what was wrong, and submit your
332updated change.
333334It is quite common for Linus to "drop" your patch without comment.
335That's the nature of the system. If he drops your patch, it could be
336due to
337* Your patch did not apply cleanly to the latest kernel version.
338* Your patch was not sufficiently discussed on linux-kernel.
339* A style issue (see section 2).
340* An e-mail formatting issue (re-read this section).
341* A technical problem with your change.
342* He gets tons of e-mail, and yours got lost in the shuffle.
343* You are being annoying.
344345When in doubt, solicit comments on linux-kernel mailing list.
34634734834911) Include PATCH in the subject
350351Due to high e-mail traffic to Linus, and to linux-kernel, it is common
352convention to prefix your subject line with [PATCH]. This lets Linus
353and other kernel developers more easily distinguish patches from other
354e-mail discussions.
35535635735812) Sign your work
359360To improve tracking of who did what, especially with patches that can
361percolate to their final resting place in the kernel through several
362layers of maintainers, we've introduced a "sign-off" procedure on
363patches that are being emailed around.
364365The sign-off is a simple line at the end of the explanation for the
366patch, which certifies that you wrote it or otherwise have the right to
367pass it on as an open-source patch. The rules are pretty simple: if you
368can certify the below:
369370 Developer's Certificate of Origin 1.1
371372 By making a contribution to this project, I certify that:
373374 (a) The contribution was created in whole or in part by me and I
375 have the right to submit it under the open source license
376 indicated in the file; or
377378 (b) The contribution is based upon previous work that, to the best
379 of my knowledge, is covered under an appropriate open source
380 license and I have the right under that license to submit that
381 work with modifications, whether created in whole or in part
382 by me, under the same open source license (unless I am
383 permitted to submit under a different license), as indicated
384 in the file; or
385386 (c) The contribution was provided directly to me by some other
387 person who certified (a), (b) or (c) and I have not modified
388 it.
389390 (d) I understand and agree that this project and the contribution
391 are public and that a record of the contribution (including all
392 personal information I submit with it, including my sign-off) is
393 maintained indefinitely and may be redistributed consistent with
394 this project or the open source license(s) involved.
395396then you just add a line saying
397398 Signed-off-by: Random J Developer <random@developer.example.org>
399400using your real name (sorry, no pseudonyms or anonymous contributions.)
401402Some people also put extra tags at the end. They'll just be ignored for
403now, but you can do this to mark internal company procedures or just
404point out some special detail about the sign-off.
405406If you are a subsystem or branch maintainer, sometimes you need to slightly
407modify patches you receive in order to merge them, because the code is not
408exactly the same in your tree and the submitters'. If you stick strictly to
409rule (c), you should ask the submitter to rediff, but this is a totally
410counter-productive waste of time and energy. Rule (b) allows you to adjust
411the code, but then it is very impolite to change one submitter's code and
412make him endorse your bugs. To solve this problem, it is recommended that
413you add a line between the last Signed-off-by header and yours, indicating
414the nature of your changes. While there is nothing mandatory about this, it
415seems like prepending the description with your mail and/or name, all
416enclosed in square brackets, is noticeable enough to make it obvious that
417you are responsible for last-minute changes. Example :
418419 Signed-off-by: Random J Developer <random@developer.example.org>
420 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
421 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
422423This practice is particularly helpful if you maintain a stable branch and
424want at the same time to credit the author, track changes, merge the fix,
425and protect the submitter from complaints. Note that under no circumstances
426can you change the author's identity (the From header), as it is the one
427which appears in the changelog.
428429Special note to back-porters: It seems to be a common and useful practice
430to insert an indication of the origin of a patch at the top of the commit
431message (just after the subject line) to facilitate tracking. For instance,
432here's what we see in 2.6-stable :
433434 Date: Tue May 13 19:10:30 2008 +0000
435436 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
437438 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
439440And here's what appears in 2.4 :
441442 Date: Tue May 13 22:12:27 2008 +0200
443444 wireless, airo: waitbusy() won't delay
445446 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
447448Whatever the format, this information provides a valuable help to people
449tracking your trees, and to people trying to trouble-shoot bugs in your
450tree.
45145245313) When to use Acked-by: and Cc:
454455The Signed-off-by: tag indicates that the signer was involved in the
456development of the patch, or that he/she was in the patch's delivery path.
457458If a person was not directly involved in the preparation or handling of a
459patch but wishes to signify and record their approval of it then they can
460arrange to have an Acked-by: line added to the patch's changelog.
461462Acked-by: is often used by the maintainer of the affected code when that
463maintainer neither contributed to nor forwarded the patch.
464465Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
466has at least reviewed the patch and has indicated acceptance. Hence patch
467mergers will sometimes manually convert an acker's "yep, looks good to me"
468into an Acked-by:.
469470Acked-by: does not necessarily indicate acknowledgement of the entire patch.
471For example, if a patch affects multiple subsystems and has an Acked-by: from
472one subsystem maintainer then this usually indicates acknowledgement of just
473the part which affects that maintainer's code. Judgement should be used here.
474When in doubt people should refer to the original discussion in the mailing
475list archives.
476477If a person has had the opportunity to comment on a patch, but has not
478provided such comments, you may optionally add a "Cc:" tag to the patch.
479This is the only tag which might be added without an explicit action by the
480person it names. This tag documents that potentially interested parties
481have been included in the discussion
48248348414) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
485486The Reported-by tag gives credit to people who find bugs and report them and it
487hopefully inspires them to help us again in the future. Please note that if
488the bug was reported in private, then ask for permission first before using the
489Reported-by tag.
490491A Tested-by: tag indicates that the patch has been successfully tested (in
492some environment) by the person named. This tag informs maintainers that
493some testing has been performed, provides a means to locate testers for
494future patches, and ensures credit for the testers.
495496Reviewed-by:, instead, indicates that the patch has been reviewed and found
497acceptable according to the Reviewer's Statement:
498499 Reviewer's statement of oversight
500501 By offering my Reviewed-by: tag, I state that:
502503 (a) I have carried out a technical review of this patch to
504 evaluate its appropriateness and readiness for inclusion into
505 the mainline kernel.
506507 (b) Any problems, concerns, or questions relating to the patch
508 have been communicated back to the submitter. I am satisfied
509 with the submitter's response to my comments.
510511 (c) While there may be things that could be improved with this
512 submission, I believe that it is, at this time, (1) a
513 worthwhile modification to the kernel, and (2) free of known
514 issues which would argue against its inclusion.
515516 (d) While I have reviewed the patch and believe it to be sound, I
517 do not (unless explicitly stated elsewhere) make any
518 warranties or guarantees that it will achieve its stated
519 purpose or function properly in any given situation.
520521A Reviewed-by tag is a statement of opinion that the patch is an
522appropriate modification of the kernel without any remaining serious
523technical issues. Any interested reviewer (who has done the work) can
524offer a Reviewed-by tag for a patch. This tag serves to give credit to
525reviewers and to inform maintainers of the degree of review which has been
526done on the patch. Reviewed-by: tags, when supplied by reviewers known to
527understand the subject area and to perform thorough reviews, will normally
528increase the likelihood of your patch getting into the kernel.
529530A Suggested-by: tag indicates that the patch idea is suggested by the person
531named and ensures credit to the person for the idea. Please note that this
532tag should not be added without the reporter's permission, especially if the
533idea was not posted in a public forum. That said, if we diligently credit our
534idea reporters, they will, hopefully, be inspired to help us again in the
535future.
536537A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
538is used to make it easy to determine where a bug originated, which can help
539review a bug fix. This tag also assists the stable kernel team in determining
540which stable kernel versions should receive your fix. This is the preferred
541method for indicating a bug fixed by the patch. See #2 above for more details.
54254354415) The canonical patch format
545546The canonical patch subject line is:
547548 Subject: [PATCH 001/123] subsystem: summary phrase
549550The canonical patch message body contains the following:
551552 - A "from" line specifying the patch author.
553554 - An empty line.
555556 - The body of the explanation, which will be copied to the
557 permanent changelog to describe this patch.
558559 - The "Signed-off-by:" lines, described above, which will
560 also go in the changelog.
561562 - A marker line containing simply "---".
563564 - Any additional comments not suitable for the changelog.
565566 - The actual patch (diff output).
567568The Subject line format makes it very easy to sort the emails
569alphabetically by subject line - pretty much any email reader will
570support that - since because the sequence number is zero-padded,
571the numerical and alphabetic sort is the same.
572573The "subsystem" in the email's Subject should identify which
574area or subsystem of the kernel is being patched.
575576The "summary phrase" in the email's Subject should concisely
577describe the patch which that email contains. The "summary
578phrase" should not be a filename. Do not use the same "summary
579phrase" for every patch in a whole patch series (where a "patch
580series" is an ordered sequence of multiple, related patches).
581582Bear in mind that the "summary phrase" of your email becomes a
583globally-unique identifier for that patch. It propagates all the way
584into the git changelog. The "summary phrase" may later be used in
585developer discussions which refer to the patch. People will want to
586google for the "summary phrase" to read discussion regarding that
587patch. It will also be the only thing that people may quickly see
588when, two or three months later, they are going through perhaps
589thousands of patches using tools such as "gitk" or "git log
590--oneline".
591592For these reasons, the "summary" must be no more than 70-75
593characters, and it must describe both what the patch changes, as well
594as why the patch might be necessary. It is challenging to be both
595succinct and descriptive, but that is what a well-written summary
596should do.
597598The "summary phrase" may be prefixed by tags enclosed in square
599brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
600considered part of the summary phrase, but describe how the patch
601should be treated. Common tags might include a version descriptor if
602the multiple versions of the patch have been sent out in response to
603comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
604comments. If there are four patches in a patch series the individual
605patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
606that developers understand the order in which the patches should be
607applied and that they have reviewed or applied all of the patches in
608the patch series.
609610A couple of example Subjects:
611612 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
613 Subject: [PATCHv2 001/207] x86: fix eflags tracking
614615The "from" line must be the very first line in the message body,
616and has the form:
617618 From: Original Author <author@example.com>
619620The "from" line specifies who will be credited as the author of the
621patch in the permanent changelog. If the "from" line is missing,
622then the "From:" line from the email header will be used to determine
623the patch author in the changelog.
624625The explanation body will be committed to the permanent source
626changelog, so should make sense to a competent reader who has long
627since forgotten the immediate details of the discussion that might
628have led to this patch. Including symptoms of the failure which the
629patch addresses (kernel log messages, oops messages, etc.) is
630especially useful for people who might be searching the commit logs
631looking for the applicable patch. If a patch fixes a compile failure,
632it may not be necessary to include _all_ of the compile failures; just
633enough that it is likely that someone searching for the patch can find
634it. As in the "summary phrase", it is important to be both succinct as
635well as descriptive.
636637The "---" marker line serves the essential purpose of marking for patch
638handling tools where the changelog message ends.
639640One good use for the additional comments after the "---" marker is for
641a diffstat, to show what files have changed, and the number of
642inserted and deleted lines per file. A diffstat is especially useful
643on bigger patches. Other comments relevant only to the moment or the
644maintainer, not suitable for the permanent changelog, should also go
645here. A good example of such comments might be "patch changelogs"
646which describe what has changed between the v1 and v2 version of the
647patch.
648649If you are going to include a diffstat after the "---" marker, please
650use diffstat options "-p 1 -w 70" so that filenames are listed from
651the top of the kernel source tree and don't use too much horizontal
652space (easily fit in 80 columns, maybe with some indentation). (git
653generates appropriate diffstats by default.)
654655See more details on the proper patch format in the following
656references.
65765865916) Sending "git pull" requests (from Linus emails)
660661Please write the git repo address and branch name alone on the same line
662so that I can't even by mistake pull from the wrong branch, and so
663that a triple-click just selects the whole thing.
664665So the proper format is something along the lines of:
666667 "Please pull from
668669 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
670671 to get these changes:"
672673so that I don't have to hunt-and-peck for the address and inevitably
674get it wrong (actually, I've only gotten it wrong a few times, and
675checking against the diffstat tells me when I get it wrong, but I'm
676just a lot more comfortable when I don't have to "look for" the right
677thing to pull, and double-check that I have the right branch-name).
678679680Please use "git diff -M --stat --summary" to generate the diffstat:
681the -M enables rename detection, and the summary enables a summary of
682new/deleted or renamed files.
683684With rename detection, the statistics are rather different [...]
685because git will notice that a fair number of the changes are renames.
686687-----------------------------------
688SECTION 2 - HINTS, TIPS, AND TRICKS
689-----------------------------------
690691This section lists many of the common "rules" associated with code
692submitted to the kernel. There are always exceptions... but you must
693have a really good reason for doing so. You could probably call this
694section Linus Computer Science 101.
6956966976981) Read Documentation/CodingStyle
699700Nuff said. If your code deviates too much from this, it is likely
701to be rejected without further review, and without comment.
702703One significant exception is when moving code from one file to
704another -- in this case you should not modify the moved code at all in
705the same patch which moves it. This clearly delineates the act of
706moving the code and your changes. This greatly aids review of the
707actual differences and allows tools to better track the history of
708the code itself.
709710Check your patches with the patch style checker prior to submission
711(scripts/checkpatch.pl). The style checker should be viewed as
712a guide not as the final word. If your code looks better with
713a violation then its probably best left alone.
714715The checker reports at three levels:
716 - ERROR: things that are very likely to be wrong
717 - WARNING: things requiring careful review
718 - CHECK: things requiring thought
719720You should be able to justify all violations that remain in your
721patch.
7227237247252) #ifdefs are ugly
726727Code cluttered with ifdefs is difficult to read and maintain. Don't do
728it. Instead, put your ifdefs in a header, and conditionally define
729'static inline' functions, or macros, which are used in the code.
730Let the compiler optimize away the "no-op" case.
731732Simple example, of poor code:
733734 dev = alloc_etherdev (sizeof(struct funky_private));
735 if (!dev)
736 return -ENODEV;
737 #ifdef CONFIG_NET_FUNKINESS
738 init_funky_net(dev);
739 #endif
740741Cleaned-up example:
742743(in header)
744 #ifndef CONFIG_NET_FUNKINESS
745 static inline void init_funky_net (struct net_device *d) {}
746 #endif
747748(in the code itself)
749 dev = alloc_etherdev (sizeof(struct funky_private));
750 if (!dev)
751 return -ENODEV;
752 init_funky_net(dev);
7537547557563) 'static inline' is better than a macro
757758Static inline functions are greatly preferred over macros.
759They provide type safety, have no length limitations, no formatting
760limitations, and under gcc they are as cheap as macros.
761762Macros should only be used for cases where a static inline is clearly
763suboptimal [there are a few, isolated cases of this in fast paths],
764or where it is impossible to use a static inline function [such as
765string-izing].
766767'static inline' is preferred over 'static __inline__', 'extern inline',
768and 'extern __inline__'.
7697707717724) Don't over-design.
773774Don't try to anticipate nebulous future cases which may or may not
775be useful: "Make it as simple as you can, and no simpler."
776777778779----------------------
780SECTION 3 - REFERENCES
781----------------------
782783Andrew Morton, "The perfect patch" (tpp).
784 <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
785786Jeff Garzik, "Linux kernel patch submission format".
787 <http://linux.yyz.us/patch-format.html>
788789Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
790 <http://www.kroah.com/log/linux/maintainer.html>
791 <http://www.kroah.com/log/linux/maintainer-02.html>
792 <http://www.kroah.com/log/linux/maintainer-03.html>
793 <http://www.kroah.com/log/linux/maintainer-04.html>
794 <http://www.kroah.com/log/linux/maintainer-05.html>
795 <http://www.kroah.com/log/linux/maintainer-06.html>
796797NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
798 <https://lkml.org/lkml/2005/7/11/336>
799800Kernel Documentation/CodingStyle:
801 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
802803Linus Torvalds's mail on the canonical patch format:
804 <http://lkml.org/lkml/2005/4/7/183>
805806Andi Kleen, "On submitting kernel patches"
807 Some strategies to get difficult or controversial changes in.
808http://halobates.de/on-submitting-patches.pdf809810--